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Tropical Storm DORIAN Forecast Discussion Number 8
2013-07-26 04:41:34| National Hurricane Center (Atlantic)
Issued at 1100 PM AST THU JUL 25 2013 000 WTNT44 KNHC 260241 TCDAT4 TROPICAL STORM DORIAN DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013 1100 PM AST THU JUL 25 2013 THE CONVECTIVE STRUCTURE OF DORIAN HAS NOT BEEN PARTICULARLY ORGANIZED THIS EVENING...AND RECENT MICROWAVE IMAGERY INDICATES THAT THE LOW-LEVEL CENTER LIES TO THE SOUTHWEST OF THE DEEP CONVECTION. A 2340 UTC ASCAT-B OVERPASS INDICATES THAT DORIAN HAS WEAKENED A BIT...AND THE INITIAL INTENSITY IS NOW 45 KT. DORIAN IS BEING DRIVEN QUICKLY WEST-NORTHWESTWARD BY A LOW- TO MID-LEVEL ANTICYCLONE OVER THE CENTRAL ATLANTIC...AND ITS ESTIMATED MOTION IS 285/17 KT. THE ANTICYCLONE IS FORECAST TO MOVE WESTWARD IN TANDEM WITH DORIAN THROUGH DAY 3...BUT THE GLOBAL MODELS THEN SUGGEST THAT THIS FEATURE WILL EVOLVE INTO A NORTHEAST-TO-SOUTHWEST ORIENTED RIDGE AXIS THAT EXTENDS ACROSS FLORIDA BY DAYS 4 AND 5. BECAUSE OF THIS PATTERN EVOLUTION...THE TRACK GUIDANCE ENVELOPE HAS SHIFTED A LITTLE SOUTHWARD ON THIS CYCLE. THE 18Z RUN OF THE GFS IS VERY SIMILAR TO THE 12Z RUN AND IS THE SOUTHERNMOST AND SLOWEST TRACK MODEL WHILE THE ECMWF IS THE NORTHERNMOST AND FASTEST. THE NHC TRACK FORECAST HAS BEEN NUDGED A BIT SOUTH OF THE PREVIOUS FORECAST TO FOLLOW THE OVERALL TREND IN THE GUIDANCE...BUT IT ENDS UP CLOSE TO THE ECMWF TRACK ON THE NORTHERN SIDE OF THE ENVELOPE. DORIAN IS EMBEDDED IN AN ENVIRONMENT OF FAST EASTERLY LOW-LEVEL FLOW AND RELATIVELY LIGHT UPPER-LEVEL WINDS...WHICH APPEARS TO BE INDUCING SOME WESTERLY TO SOUTHWESTERLY SHEAR IN THE LAYER BELOW THE CIRRUS OUTFLOW. SINCE THE FORWARD SPEED OF THE CYCLONE IS NOT EXPECTED TO SLOW DOWN ANY TIME SOON...DORIAN COULD EXPERIENCE PERSISTENT SHEAR FOR THE NEXT FEW DAYS. ON TOP OF THAT...MID-LEVEL RELATIVE HUMIDITIES ARE EXPECTED TO DECREASE...AND THE DRY AIR COULD INHIBIT DEEP CONVECTION. NONE OF THE GUIDANCE SHOWS MUCH CHANGE IN INTENSITY DURING THE NEXT FEW DAYS...SO THE OFFICIAL FORECAST WILL KEEP THE WINDS FLATLINED AT 45 KT THROUGH DAY 3 WITH NOT MUCH STRENGTHENING THEREAFTER. THIS FORECAST IS A BIT LOWER THAN THE PREVIOUS ONE...PARTIALLY TO ACCOUNT FOR THE LOWER INITIAL INTENSITY. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 16.6N 39.6W 45 KT 50 MPH 12H 26/1200Z 17.2N 42.4W 45 KT 50 MPH 24H 27/0000Z 17.8N 46.4W 45 KT 50 MPH 36H 27/1200Z 18.3N 50.4W 45 KT 50 MPH 48H 28/0000Z 19.0N 54.3W 45 KT 50 MPH 72H 29/0000Z 20.0N 61.5W 45 KT 50 MPH 96H 30/0000Z 20.5N 67.5W 50 KT 60 MPH 120H 31/0000Z 21.0N 72.0W 50 KT 60 MPH $$ FORECASTER BERG
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